1. Field of the Invention
This invention relates to methods of treating single cell microorganisms to recover functional proteins. More particularly, it relates to a method of solubilizing the entire cell to yield a solution from which the various functional cell materials can be recovered.
2. Description of the Prior Art
Single cell protein materials such as yeasts have constituents which are highly desirable for many varied uses, the most important constituent being proteins. For example, spray-dried Candida utilis yeast typically contains about 52% protein. This protein is predominently located in the cytoplasmic material within the cell wall. The cell wall itself is for the most part made up of two layers, each of which has a polysaccharide network structure. The outermost layer is mannan, which is a polysaccharide derived from mannose. The inner network is glucan, which is derived from glucose. It is highly desirable to isolate the proteinaceous cell components from the others to obtain a concentrate or isolate material, or fractions thereof, which can be used in a variety of food applications.
Aside from nutritional uses for which protein materials have obvious utility, food uses for single cell protein materials are generally determined by their exhibition of certain desirable properties, commonly referred to broadly as "functionality." The functionality of a material is exhibited by the ability of the material to alter the characteristics of the food product into which the material is incorporated. These materials may enhance certain flavors such as cheese, meat, chocolate, etc., or they may alter other physical properties such as whippability, coagulability, color, texture, etc. In general, much of the functional nature of single-cell materials is associated with the availability of the internal cellular components, particularly the proteinaceous materials. Although whole undamaged cells do exhibit some desirable properties, the functionality of the cell can be greatly enhanced by exposing some of the internal cell contents.
Recovery of the proteins from the whole cell has been typically carried out previously by first breaking open the cell wall by mechanical means and then subjecting the broken cell mass to an extraction. Homogenization of the cells is a common physical method for opening the cells, but such a method is expensive and inefficient.
Satisfactory chemical methods for breaking the cell wall have not been developed, although chemical means for cleaving certain carbohydrates such as sugars and some polysaccharides are known in the art. It is known, for example, that periodate (IO.sub.4.sup.-) will oxidize sugars according to the reaction: ##STR1## (See "Experimental Biochemistry" pages 6-8, 14-16, 27-29, by John M. Clark, Jr. published by W. H. Freeman and Company, San Francisco and London). This reaction has been used as an analytical tool for determining the structure and polyhydroxyl character of sugars and polysaccharides. However, the applicability of such a method toward recovering proteins from single-cell microorganisms has not been suggested.
It would be desirable to provide a simple chemical means for disrupting the cell wall without any substantial harm to the cell contents. If the cell wall could be perforated, but without being completely broken, the resulting whole cell product would have improved functionality. If the entire cell could be dissolved in an aqueous solution, selected cell components could be readily and selectively recovered by various suitable means such as precipitation or fractionation. Alternatively, because of the large amount of protein present, the cell solution could be used as a starting material for producing a textured product by extruding the solution into an acid bath to precipitate the proteins and form a textured extrudate.
Therefore it is an object of this invention to provide a mild treatment for modifying the cell wall of single-cell microorganisms.
It is a further object of this invention to provide a method for recovering protein material from single-cell microorganisms without resorting to mechanical breakage of the cell wall.
It is another object of this invention to provide a method for completely dissolving the entire cell in an aqueous solution.
These and other objects will become apparent from further reading of this specification.